The present invention relates to a mechanical seal system for centrifugal process and transfer pumps, and more particularly to such pumps which include a stuffing box and packing gland.
Generally, the sealing of pumps and shafts has been by mechanical seals. A typical mechanical seal would include a stationary sealing ring sealed by an o-ring gasket to the housing and a spring loaded sealing member secured to the shaft or a sleeve on the shaft that rotates with the shaft. The rotating sealing member is usually spring loaded in some fashion to insure that as the sealing surfaces wear the spring will keep the rotating sealing member engaged with the stationary sealing ring. Such mechanical seals are frequently used to seal stuffing boxes of process and transfer pumps in various industries including oil and gas operations, chemical process, food process and others.
Sealing pumps and turbine shafts from products being pumped becomes extremely important with many new designs of pumps and turbines running at higher speeds, pressures and temperatures thus exacerbating the problems of high maintenance costs, loss of products safety and environmental protection.
Some mechanical seals utilize a soft material spring-loaded against a harder surface with one of the sealing materials stationary and the other rotating with the shaft being sealed. As the soft material wears away the spring constantly urges the soft material against the hard surface. If the spring can no longer maintain engagement between the soft material and the hard surface the seal is lost. Also, if the soft sealing material wears away it may break or leak even though the spring has sufficient biasing force. As solutions to these problems, various sealing arrangement have been proposed and developed which include both labyrinth seals and lip seals for sealing bearing housings to shafts to prevent lubricants from moving outside of the housing along the shaft and to eliminate the movement of contaminates into the bearing areas and lubricant within the housing.
U.S. Pat. Nos. 4,022,479; 4,466,620; and 4,706,968 all granted to David C. Orlowski disclose the improvements made in labyrinth seals. Typically, in the labyrinth seal of Orlowski one part of the mechanical labyrinth seal is affixed to the shaft and one part of the seal is affixed to the housing. The interface or point of mesh between the two parts of the mechanical seal is often designed to provide a labyrinth or tortuous path at the point of close proximity with the object of obtaining a seal between the housing and shaft.
The sealing arrangement described in Pat. No. 4,706,968 of Orlowski is designed to aid in overcoming axial displacement which would cause problems with the two piece labyrinth mechanical seal.
U.S. Pat. No. 4,337,951 granted to Perego discloses another mechanical seal which includes a labyrinth, as well as, an end face seal in which pressure is used to cause the sealing member to engage the sealing surface.
An automobile water pump using a lip seal is disclosed in U.S. Pat. No. 4,921,260. The purpose of this seal is to prevent the generation of abnormal sounds and provide a good sealing effect for a water pump. Primarily, Tankenaka is concerned with eliminating resonant parts such as coil springs of conventional sealing devices in order to prevent the generation of abnormal noises. He also describes that a lip type sealing device is known in sealing an automotive compressor which uses no coil springs.
Another patent, U.S. Pat. No. 2,990,220 to Malone discloses a lip seal for the track rollers on a track laying vehicle to avoid foreign material getting into the bearing and to retain the grease in the bearing.
U.S. Pat. No. 4,572,517 of Rockwood discloses a labyrinth ring seal and housing mounting means which are alleged improvements in labyrinth ring seals. Rockwood provides a stationary sealing ring and a rotating sealing ring having several different diameter walls which mate with each other to prevent lubricant from moving from the housing and to prevent material tending to enter the housing.
Italian Patent No. 500,739, issued to Valentini discloses a sealing arrangement for a centrifugal pump. It describes a spring-loaded clutch plate engaging a collar. The collar is stationary relative to the shaft while the clutch plate rotates with the shaft and the collar gasket is worn away to maintain the seal. The need for replacement of this gasket is indicated by its expulsion through the discharge outlet. A seal cage consisting of a leather gasket contained in a metal sleeve protects the ball bearing supporting the shaft from contamination.
British Patent No. 1,038,019 discloses a shaft sleeve of copper which is covered with a thin layer of hard chromium.
U.S. Pat. No. 3,796,510, issued to Korrenn discloses a shaft mounting for water pumps with two sets of frustoconical bearing rollers for supporting the shaft and are sealed at each end to confine the bearing lubricant therein. An elastic sealing ring is provided to help contain the working fluid of the pump from traveling down the shaft. The bushing containing the frustoconical bearings abuts one side of the collar and the elastic sealing ring abuts the other side of the collar to help contain the working fluid of the pump. The collar is vented to the atmosphere to discharge any working fluid leaking past the seal.
U.S. Pat. No. 3,711,218, issued to Kennel et al discloses a centrifugal pump having a housing section surrounding the impeller of the pump. The housing has a body portion which comprises a sealing device or stuffing box through which extends the impeller shaft. A bearing section connected to the housing section has a pair of spaced apart ball bearings which support the impeller shaft for rotation. It will be observed that no roller bearing is contained within the stuffing box which illustrate some kind of packing around the shaft therein.
However, all of the designs still suffer the problems associated with shaft whip or lack of concentricity between the shaft and the seal at the sealing surface. Consequently the seals suffer excessive wear and require frequent maintenance.